Horizons and faults are fundamental geologic features that describe the geology, geometry, and topology of the subsurface of the earth. Faults compartmentalize the subsurface and are indicators of deformation over geologic time. Faults can act as permeable conduits or impermeable seals affecting the flow of subsurface fluids and gases. Thus, the understanding of faults in an area is often useful for the prospecting of oil and natural gas. Furthermore, seismologists are also tasked with identifying geologic fault hazards that are dangerous when drilling and extracting oil and natural gas. Hence, rapid and accurate mapping of geologic faults has high economic and safety value.
There are a variety of methods used for producing images that outline subsurface terrain. One technique that is often used involves radiating energy into the ground and measuring the reflections at various sensors. This imaging technique is referred to as the seismic method. Using the data acquired by the seismic method, three-dimensional seismic images of the underground geology, geometry, and topology can be created. Generally, fault lines are depicted in these seismic images by visible lines. Thus, a seismologist may study these lines to determine fault locations for use in prospecting.
Various methods have been developed and used to analyze three-dimensional seismic images. For example, the coherence cube method was developed to enhance fault features in seismic images. The coherence cube method in turn has lead to a variety of methods for extracting, or interpreting, fault traces or surfaces from fault-enhanced seismic images. These methods tend to be done manually. Manual fault interpretation is usually performed by a trained geologist manually identifying image points that correspond to particular faults and interpolating these points with smooth curves or surfaces, independent of the fault image. High fidelity fault curves or surfaces can be produced only by manually identifying numerous fault points in the fault image. Manual interpretation of geological faults in seismic images is a tedious, error-prone and largely non-reproducible process.
The problems associated with manual fault interpretation and the rise in computing power has led to the introduction of various automated methods for performing fault interpretation. One method for automatically processing a fault-enhanced three-dimensional seismic image is described in U.S. Pat. No. 5,987,388 to Crawford et al. In the method of Crawford, individual two-dimensional slices of a three-dimensional seismic image are processed in an attempt to trace fault lines. This method is not conducive to interpreter control of the extracted surfaces and tends to create false positive surfaces from the edges of the seismic survey and from geologically unreasonable coherent noise in the image. The extracted models, being cluttered with false fault surfaces, are frequently not useful to analysts.
Since faults quite often occur in and cause noisy images, a mixture of manual and automated interpretation is required. What is needed is a semi-automated computer-based process that reduces the time consuming nature of fault interpretation, while simultaneously increasing the fidelity and reproducibility of the extracted fault surfaces, and at the same time allowing an analyst to manually interpret and modify the automatically extracted curves and surfaces in regions of poor image quality.
One method for extracting curves in 2-D images is to use a shortest path algorithm. This method, variously known as “Intelligent Scissors” or “Livewire”, has proven useful for image segmentation in the commercial product Photoshop®. It has not, however, previously been employed for fault interpretation of seismic images.
It is with these and other issues in mind that various aspects of the present disclosure were developed.